As is well known, semiconductor products are of great importance and semiconductor chips as a typical example thereof are manufactured, for example, by preparing silicon wafers by slicing silicon single crystals to predetermined thickness and then forming various circuits on the silicon wafers.
The various circuits are formed into circuit patterns by sputtering or etching on silicon wafers and, since sputtering or etching is conducted at a high temperature and corrosive gases are sometimes used, they are preferably made of ceramic sintering products.
Such ceramic heaters comprise, as main constituent elements, a ceramic substrate and, a heat generation body disposed substantially over the entire rear face of the substrate, for example, a resistor pattern that generates heat upon current supply.
In existent ceramic heaters having such a constitution, it is preferred that insertion holes for lift pins for receiving and handing wafers (for example as disclosed in Japanese Patent Application Laid-open No. Hei 11-40330) or vacuum suction holes for heating the wafer in a state closely adhered to a heating surface are formed preferably, because the former is advantageous for conducting charge and discharge of wafers to and from the ceramic heater and the latter is advantageous for conducting rapid heating.
Further, since it is necessary for temperature control of the ceramic heater, recesses are disposed on the rear face of the ceramic heater for attaching temperature control parts such as thermocouple or thermal fuse and such temperature control parts are attached to the recesses.
However, the present inventors have found that the temperature becomes ununiform or lower temperature spots in which the temperature lowers locally are formed at the periphery of through holes such as the insertion holes or vacuum suction holes and in the recesses.
Such low temperature spots may possibly cause thermal shocks to the wafer upon heat-drying treatment. Further, the bottom of the recess is a portion in direct contact with the temperature control parts, for example, a temperature measuring element and, if the temperature is not uniform at the portion of the bottom, it is not preferred since the controllability of the temperature control part is lowered.
Further, a resin is sometimes coated on the wafer, which is exposed for development and thermally cured, but there was a problem that the cure of the resin was not uniform.
It is an object of the present invention to provide a ceramic heater capable of reducing the ununiformity of the temperature at the periphery of through holes such as insertion holes or vacuum suction holes thereby protecting the wafer against thermal shocks. Further, it is a subject of the present invention to provide a ceramic heater improved with the controllability for the temperature control parts such as thermocouples or thermal fuses.
A further object of the present invention is to provide a ceramic heater capable of uniformly curing resins.